1. Field of the Invention
The invention relates to an aluminum rolled semifinished product in the form of sheets, strips, or foils, composed of an aluminum alloy of the AlFeMn type with a uniform, fine-grained structure, and a process for its manufacture.
2. Description of Prior Art
It is known from Altenpohl "Looking at Aluminum from the Inside," 2nd edition, 1970, page 102, that when making semifinished products which must fulfill strict requirements as to workability, full annealing at temperatures between 550.degree. and 630.degree. C. must be performed. Annealing time depends on the grain size and the diffusion rate of the critical alloy component. If, at the maximum possible full annealing temperature according to the phase diagram, one alloy component is no longer completely soluble in aluminum, a finely distributed precipitation takes place in the interior and at the grain boundaries of the cast grains. The influence of cooling following full annealing is shown, on page 101 of the references, for an alloy with 1% Mn, 0.67% Fe, and 0.16% Si with the remainder being Al in three structural patterns.
The same publication, last page, provides an overview of processes in the structure during the most important stages in the manufacture of rolled semifinished products. After cold working, soft annealing is performed at temperatures of approximately 250.degree. to 500.degree. C. to improve workability.
Deformation hardening is eliminated by recrystallization and numerous fine deposits of alloy metals appear in the microstrcuture, which are precipitated during soft annealing.
In aluminum rolled products containing the known alloy, after conventional manufacturing methods are employed with final annealing, grains on the order of 15-100 .mu.m are produced; the average diameter of all the existing grains is given as the grain size.
In addition, the softening process is such that material states with high strength values and simultaneous high elongation values can be achieved only by using special measures such as high cooling rate, for example. Usually elongation is not sufficient when the strength is sufficiently high to manufacture deep-drawable material, as for example, flat strip material, or the strength is too low while elongation is sufficient.